1. Field of the Invention
The invention relates generally to a valve and more particularly to a shut-off valve of a type suitable for use in a vacuum line. The invention further relates to an installation including such a valve, in particular a milking installation.
2. Description of the Related Art
Valves are known in which a valve element is located in a flow passage. The valve can close by seating of the valve element on a valve seat within the passage. Opening of the valve may be achieved by movement of an engaging element to move the valve element away from the seat. Such a valve is known from U.S. Pat. No. 6,149,125 which uses a hydraulic arrangement to engage the valve element. A further device is known from U.S. Pat. No. 2,942,618, which uses a magnet to hold the valve element in an open position. The valve element is released by the magnet in response to pressure increases or decreases outside a given range. The pressure range is adjusted by controlling the biasing force on a pair of plungers. In order to release the valve element from a closed position, a complicated arrangement of valves may be provided.
There is thus a need for a simpler and cheaper construction to realize such control.